1. Field of the Invention
The present invention relates to analog signal processing. In particular, the present invention relates to analog mixers, such as those used for up-conversion of a baseband signal.
2. Discussion of the Related Art
One mixer circuit known in the prior art is the Gilbert cell mixer, such as Gilbert cell mixer 200 shown in FIG. 2. As shown in FIG. 2, Gilbert cell 200 includes differential pairs formed, respectively, by NPN transistors Q1 and Q2 and NPN transistors Q3 and Q4, a voltage-to-current conversion stage formed by NPN transistors Q5 and Q6 and resistors Rp and Rm, and a tail current source formed by NPN transistor Q7 and resistor Rb. Gilbert cell mixer 200 suffers from a relatively high power supply voltage requirement and noise from NPN transistors Q5 and Q6 used in the voltage-to-current conversion stage.
U.S. Pat. No. 7,308,244 to Chang et al. (“Chang”) discloses a low voltage mixer. Specifically, at FIG. 3 of Chang, Chang discloses a mixer with reduced voltage headroom. Chang does not disclose generating quadrature signals from a passive circuit.
U.S. Pat. No. 6,959,180 to Ji (“Ji”) discloses a mixer with a low temperature co-fired ceramic (LTCC) structure.